8 ms·

Hydrogen electrolysys can't be done efficiently at home. And the efficiency even in industrial plants is pretty bad, about 50% to produce hydrogen compressed fo

Hydrogen electrolysys can't be done efficiently at home. And the efficiency even in industrial plants is pretty bad, about 50% to produce hydrogen compressed for car use, and that doesn't include the fuel cell efficiency that brings the total efficiency to about 30%. Batteries have much better efficiency.

darksaints 7y ago
I have efficiently done it at an industrial lab with commonly available industrial electricity rates ($.065/kWh). 93% efficiency using a solid oxide cell that was made in 2008. I don't know where you're getting your information but it's wrong. $0.116/kWh after conversion back into electricity. If I were doing it at home with residential rates, I would be paying $0.125/kWh, which is still feasible, but more expensive than gasoline at the moment. With the way solar prices are dropping, that won't last long.
- tigershark 7y ago
  https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficiency https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficien... "Efficiency of modern hydrogen generators is measured by energy consumed per standard volume of hydrogen (MJ/m3), assuming standard temperature and pressure of the H2. The lower the energy used by a generator, the higher its efficiency would be; a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen,[23] 12,749 joules per litre (12.75 MJ/m3). Practical electrolysis (using a rotating electrolyser at 15 bar pressure) may consume 50 kW⋅h/kg (180 MJ/kg), and a further 15 kW⋅h (54 MJ) if the hydrogen is compressed for use in hydrogen cars." What about your sources for 93% efficiency?
  - darksaints 7y ago
    93% is what I got in my own experiments with an used cell I bought that was made in 2008. My cell is a slight materials variant of the NASA BSC cell which was also tested at 93% efficiency. https://ntrs.nasa.gov/search.jsp?R=20090013708 https://ntrs.nasa.gov/search.jsp?R=20090013708 Here is a commercially available cell stack that is getting 88% efficiency, despite being a reversible cell (ie not optimized for electrolysis). http://www.helmeth.eu/index.php/technologies/high-temperature-electrolysis-cell-soec http://www.helmeth.eu/index.php/technologies/high-temperatur... This research system has already demonstrated 75% efficiency round-trip. That is electricity-to-hydrogen-to-electricity. 97% efficient in electrolysis alone. https://www.nature.com/articles/s41560-019-0333-2 https://www.nature.com/articles/s41560-019-0333-2
    - tigershark 7y ago
      Even with a 93% efficiency adding the energy needed to compress the hydrogen and the fuel cell efficiency you arrive at an efficiency of 48%, pretty much half as the batteries.
      - darksaints 7y ago
        I can dispute those numbers too but that is beside the point. Batteries are probably good enough in energy density for most car users, and they do have an efficiency advantage (not as great as you're trying to portray but still better). For 99% of car buyers, that's a better option. But fuel cells still have a place where energy density is a major concern. That's likely to be the case for commercial vehicles, where long recharge times and low ranges are unacceptable.

darksaints 7y ago

I have efficiently done it at an industrial lab with commonly available industrial electricity rates ($.065/kWh). 93% efficiency using a solid oxide cell that was made in 2008. I don't know where you're getting your information but it's wrong. $0.116/kWh after conversion back into electricity. If I were doing it at home with residential rates, I would be paying $0.125/kWh, which is still feasible, but more expensive than gasoline at the moment. With the way solar prices are dropping, that won't last long.

tigershark 7y ago
https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficiency https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficien... "Efficiency of modern hydrogen generators is measured by energy consumed per standard volume of hydrogen (MJ/m3), assuming standard temperature and pressure of the H2. The lower the energy used by a generator, the higher its efficiency would be; a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen,[23] 12,749 joules per litre (12.75 MJ/m3). Practical electrolysis (using a rotating electrolyser at 15 bar pressure) may consume 50 kW⋅h/kg (180 MJ/kg), and a further 15 kW⋅h (54 MJ) if the hydrogen is compressed for use in hydrogen cars." What about your sources for 93% efficiency?
- darksaints 7y ago
  93% is what I got in my own experiments with an used cell I bought that was made in 2008. My cell is a slight materials variant of the NASA BSC cell which was also tested at 93% efficiency. https://ntrs.nasa.gov/search.jsp?R=20090013708 https://ntrs.nasa.gov/search.jsp?R=20090013708 Here is a commercially available cell stack that is getting 88% efficiency, despite being a reversible cell (ie not optimized for electrolysis). http://www.helmeth.eu/index.php/technologies/high-temperature-electrolysis-cell-soec http://www.helmeth.eu/index.php/technologies/high-temperatur... This research system has already demonstrated 75% efficiency round-trip. That is electricity-to-hydrogen-to-electricity. 97% efficient in electrolysis alone. https://www.nature.com/articles/s41560-019-0333-2 https://www.nature.com/articles/s41560-019-0333-2
  - tigershark 7y ago
    Even with a 93% efficiency adding the energy needed to compress the hydrogen and the fuel cell efficiency you arrive at an efficiency of 48%, pretty much half as the batteries.
    - darksaints 7y ago
      I can dispute those numbers too but that is beside the point. Batteries are probably good enough in energy density for most car users, and they do have an efficiency advantage (not as great as you're trying to portray but still better). For 99% of car buyers, that's a better option. But fuel cells still have a place where energy density is a major concern. That's likely to be the case for commercial vehicles, where long recharge times and low ranges are unacceptable.